There already exist systems for testing for the correct setting up of switchpaths through a switching network. In the case of time-division switching networks, one method involves verifying correct transmission of digital samples through the stages of the network. This known method provides two types of test:
passive test: samples are taken from the network input and the output corresponding to the switchpath to be tested, and are then compared;
active test: a sample is injected at the input and retrieved from the output for comparison.
Known systems of this type have disadvantages. The system for selecting the test points is sometimes that used to control the switching network under normal circumstances, in which case the units under test must be isolated from traffic. In other cases an independent system is provided, resulting in a significant increase in complexity.
In the case of a time-division switching network, the known test systems operate synchronously with the switching network control units. They are necessarily located after units for synchronising the incoming time-division multiplex links. Thus these synchronisation units are not tested for correct operation.
The invention is intended to provide a test system which simplifies selection of test points according to their geographical location, the stage of the network and the required test mode, providing for executing tests ahead of the synchronising units and offering great flexibility in terms of the interchange of messages with the control units of the switching centre.